As shown in FIG. 1(a), a tongue 1 used in a seat belt system for an automobile is used by being attached to a seat belt (woven belt) 3 in the seat belt system. While in use, the tongue 1 is connected to a buckle 7 attached to an end portion of a fixed belt 5 in the seal belt system. As shown in FIG. 1(b), a general structure of the tongue 1 is that: an insertion part 13 to be inserted in the buckle 7 is integrally provided in a projecting manner on a tongue main body 11 including a seat belt insertion hole 9 in which to insert the seat belt 3; and a lock hole 13a, to which a lock piece (not illustrated) included in the buckle 7 is capable of being locked, is provided in the neighborhood of a front end portion of this insertion part 13.
In addition, the general structure of the tongue 1 is that, as shown in FIG. 1(b), the surfaces of an area surrounding the seat belt insertion hole 9 included in the tongue main body 11 are covered with a molded resin 15. Moreover, as shown in FIG. 1(c), a tongue has been developed which has a structure in which a curved part 17 whose cross-section is shaped almost like a letter J is formed in a part of the belt insertion hole 19 instead of using the molded resin. Such a technique has been disclosed, for instance, in Japanese Patent Official Gazette: Japanese Patent No. 3440063 (Patent Document 1).
The tongue 1 of the above-described type is obtained as follows. First of all, a tongue material is produced by applying a punching process and a forming process to a metal plate by use of a pressing machine. Subsequently, as a surface treatment, a plating process is applied to the tongue material. Thereafter, the tongue material is covered with a molded resin. In a pressing process using a pressing machine, very small scraps, which are produced during the pressing process, and the like sometimes fall on the metal plate, so that very small bruises, although having no influence on the strength of the tongue itself, are caused in the surfaces of the tongue 1. Furthermore, while tongues 1 are transferred to an ensuing step in the manufacturing process, scratches, scratched marks and the like are sometimes caused in the surfaces of the tongues 1 as a result of mutual contacts between the tongues 1.
Very small bruises, scratches and the like having no influence on a tongue 1 do not matter as long as they are in an area covered with the molded resin 15 and thus look less conspicuous. On the contrary, if very small bruises, scratches and the like of the above-described type are found in any one surface of the insertion part 13 of the tongue 1 in the final stage after the molded resin 15 is molded, such a tongue 1 is discarded as a defective product. That is because: the scratches and the like look more conspicuous against the surface of the insertion part 13 which is solid and glazed; and the conspicuousness deteriorates the aesthetic appearance quality. The discard rate of tongues is approximately several percent to ten percent. This causes a problem of low yields. For this reason, the enhancement of the yields has been awaited for. In addition, it has been demanded that the bonding strength (connecting strength) between the tongue main body and the molded resin should be further increased in accordance with the material of the molded resin.
The present invention has been made for the purpose of solving the above-described problems. A first object of the present invention is to provide a tongue and a method of manufacturing the same, the tongue being capable of improving the aesthetic appearance quality by preventing scratches or the like from being caused in any one surface of the insertion part of the tongue.
A second object of the present invention is to provide a tongue and a method of manufacturing the same, the tongue being capable of improving a bonding strength (connecting strength) with the molded resin by increasing its surface area with multiple convex parts or concave parts.